FreeBSD/Linux Kernel Cross Reference
sys/libkern/mcount.c

     /*-
      * SPDX-License-Identifier: BSD-3-Clause
      *
      * Copyright (c) 1983, 1992, 1993
      *      The Regents of the University of California.  All rights reserved.
      *
      * Redistribution and use in source and binary forms, with or without
      * modification, are permitted provided that the following conditions
      * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     * 3. Neither the name of the University nor the names of its contributors
     *    may be used to endorse or promote products derived from this software
     *    without specific prior written permission.
     *
     * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     */
    
    #include <sys/cdefs.h>
    __FBSDID("$FreeBSD$");
    
    #include <sys/param.h>
    #include <sys/gmon.h>
    #ifdef _KERNEL
    #ifndef GUPROF
    #include <sys/systm.h>
    #endif
    #include <vm/vm.h>
    #include <vm/vm_param.h>
    #include <vm/pmap.h>
    #endif
    
    /*
     * mcount is called on entry to each function compiled with the profiling
     * switch set.  _mcount(), which is declared in a machine-dependent way
     * with _MCOUNT_DECL, does the actual work and is either inlined into a
     * C routine or called by an assembly stub.  In any case, this magic is
     * taken care of by the MCOUNT definition in <machine/profile.h>.
     *
     * _mcount updates data structures that represent traversals of the
     * program's call graph edges.  frompc and selfpc are the return
     * address and function address that represents the given call graph edge.
     *
     * Note: the original BSD code used the same variable (frompcindex) for
     * both frompcindex and frompc.  Any reasonable, modern compiler will
     * perform this optimization.
     */
    /* _mcount; may be static, inline, etc */
    _MCOUNT_DECL(uintfptr_t frompc, uintfptr_t selfpc)
    {
    #ifdef GUPROF
            int delta;
    #endif
            fptrdiff_t frompci;
            u_short *frompcindex;
            struct tostruct *top, *prevtop;
            struct gmonparam *p;
            long toindex;
    #ifdef _KERNEL
            MCOUNT_DECL(s)
    #endif
    
            p = &_gmonparam;
    #ifndef GUPROF                  /* XXX */
            /*
             * check that we are profiling
             * and that we aren't recursively invoked.
             */
            if (p->state != GMON_PROF_ON)
                    return;
    #endif
    #ifdef _KERNEL
            MCOUNT_ENTER(s);
    #else
            p->state = GMON_PROF_BUSY;
    #endif
    
    #ifdef _KERNEL
            /* De-relocate any addresses in a (single) trampoline. */
    #ifdef MCOUNT_DETRAMP
            MCOUNT_DETRAMP(frompc);
            MCOUNT_DETRAMP(selfpc);
    #endif
            /*
             * When we are called from an exception handler, frompc may be
             * a user address.  Convert such frompc's to some representation
            * in kernel address space.
            */
   #ifdef MCOUNT_FROMPC_USER
           frompc = MCOUNT_FROMPC_USER(frompc);
   #elif defined(MCOUNT_USERPC)
           /*
            * For separate address spaces, we can only guess that addresses
            * in the range known to us are actually kernel addresses.  Outside
            * of this range, conerting to the user address is fail-safe.
            */
           if (frompc < p->lowpc || frompc - p->lowpc >= p->textsize)
                   frompc = MCOUNT_USERPC;
   #endif
   #endif /* _KERNEL */
   
           frompci = frompc - p->lowpc;
           if (frompci >= p->textsize)
                   goto done;
   
   #ifdef GUPROF
           if (p->state == GMON_PROF_HIRES) {
                   /*
                    * Count the time since cputime() was previously called
                    * against `frompc'.  Compensate for overheads.
                    *
                    * cputime() sets its prev_count variable to the count when
                    * it is called.  This in effect starts a counter for
                    * the next period of execution (normally from now until 
                    * the next call to mcount() or mexitcount()).  We set
                    * cputime_bias to compensate for our own overhead.
                    *
                    * We use the usual sampling counters since they can be
                    * located efficiently.  4-byte counters are usually
                    * necessary.  gprof will add up the scattered counts
                    * just like it does for statistical profiling.  All
                    * counts are signed so that underflow in the subtractions
                    * doesn't matter much (negative counts are normally
                    * compensated for by larger counts elsewhere).  Underflow
                    * shouldn't occur, but may be caused by slightly wrong
                    * calibrations or from not clearing cputime_bias.
                    */
                   delta = cputime() - cputime_bias - p->mcount_pre_overhead;
                   cputime_bias = p->mcount_post_overhead;
                   KCOUNT(p, frompci) += delta;
                   *p->cputime_count += p->cputime_overhead;
                   *p->mcount_count += p->mcount_overhead;
           }
   #endif /* GUPROF */
   
   #ifdef _KERNEL
           /*
            * When we are called from an exception handler, frompc is faked
            * to be for where the exception occurred.  We've just solidified
            * the count for there.  Now convert frompci to an index that
            * represents the kind of exception so that interruptions appear
            * in the call graph as calls from those index instead of calls
            * from all over.
            */
           frompc = MCOUNT_FROMPC_INTR(selfpc);
           if ((frompc - p->lowpc) < p->textsize)
                   frompci = frompc - p->lowpc;
   #endif
   
           /*
            * check that frompc is a reasonable pc value.
            * for example: signal catchers get called from the stack,
            *              not from text space.  too bad.
            */
           if (frompci >= p->textsize)
                   goto done;
   
           frompcindex = &p->froms[frompci / (p->hashfraction * sizeof(*p->froms))];
           toindex = *frompcindex;
           if (toindex == 0) {
                   /*
                    *      first time traversing this arc
                    */
                   toindex = ++p->tos[0].link;
                   if (toindex >= p->tolimit)
                           /* halt further profiling */
                           goto overflow;
   
                   *frompcindex = toindex;
                   top = &p->tos[toindex];
                   top->selfpc = selfpc;
                   top->count = 1;
                   top->link = 0;
                   goto done;
           }
           top = &p->tos[toindex];
           if (top->selfpc == selfpc) {
                   /*
                    * arc at front of chain; usual case.
                    */
                   top->count++;
                   goto done;
           }
           /*
            * have to go looking down chain for it.
            * top points to what we are looking at,
            * prevtop points to previous top.
            * we know it is not at the head of the chain.
            */
           for (; /* goto done */; ) {
                   if (top->link == 0) {
                           /*
                            * top is end of the chain and none of the chain
                            * had top->selfpc == selfpc.
                            * so we allocate a new tostruct
                            * and link it to the head of the chain.
                            */
                           toindex = ++p->tos[0].link;
                           if (toindex >= p->tolimit)
                                   goto overflow;
   
                           top = &p->tos[toindex];
                           top->selfpc = selfpc;
                           top->count = 1;
                           top->link = *frompcindex;
                           *frompcindex = toindex;
                           goto done;
                   }
                   /*
                    * otherwise, check the next arc on the chain.
                    */
                   prevtop = top;
                   top = &p->tos[top->link];
                   if (top->selfpc == selfpc) {
                           /*
                            * there it is.
                            * increment its count
                            * move it to the head of the chain.
                            */
                           top->count++;
                           toindex = prevtop->link;
                           prevtop->link = top->link;
                           top->link = *frompcindex;
                           *frompcindex = toindex;
                           goto done;
                   }
           }
   done:
   #ifdef _KERNEL
           MCOUNT_EXIT(s);
   #else
           p->state = GMON_PROF_ON;
   #endif
           return;
   overflow:
           p->state = GMON_PROF_ERROR;
   #ifdef _KERNEL
           MCOUNT_EXIT(s);
   #endif
           return;
   }
   
   /*
    * Actual definition of mcount function.  Defined in <machine/profile.h>,
    * which is included by <sys/gmon.h>.
    */
   MCOUNT
   
   #ifdef GUPROF
   void
   mexitcount(uintfptr_t selfpc)
   {
           struct gmonparam *p;
           uintfptr_t selfpcdiff;
   
           p = &_gmonparam;
   #ifdef MCOUNT_DETRAMP
           MCOUNT_DETRAMP(selfpc);
   #endif
           selfpcdiff = selfpc - (uintfptr_t)p->lowpc;
           if (selfpcdiff < p->textsize) {
                   int delta;
   
                   /*
                    * Count the time since cputime() was previously called
                    * against `selfpc'.  Compensate for overheads.
                    */
                   delta = cputime() - cputime_bias - p->mexitcount_pre_overhead;
                   cputime_bias = p->mexitcount_post_overhead;
                   KCOUNT(p, selfpcdiff) += delta;
                   *p->cputime_count += p->cputime_overhead;
                   *p->mexitcount_count += p->mexitcount_overhead;
           }
   }
   
   #ifndef __GNUCLIKE_ASM
   #error "This file uses null asms to prevent timing loops being optimized away."
   #endif
   
   void
   empty_loop(void)
   {
           int i;
   
           for (i = 0; i < CALIB_SCALE; i++)
                   __asm __volatile("");
   }
   
   void
   nullfunc(void)
   {
           __asm __volatile("");
   }
   
   void
   nullfunc_loop(void)
   {
           int i;
   
           for (i = 0; i < CALIB_SCALE; i++)
                   nullfunc();
   }
   #endif /* GUPROF */

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